1. Field of the Invention
The present invention relates to liquid crystal displaying techniques, and in particular to a backlight module for 3D displaying and an LED (Light-Emitting Diode) light bar.
2. The Related Arts
With the progress of 3D technology, television having 3D displaying function is now becoming the main stream. The commonly known 3D displaying modes include shutter glass and film-type patterned retarder (FPR).
The shutter glass 3D displaying is effected with scanning backlight in combination with panel pixel scanning. Backlighting is often sectionalized so that a side-edge LED light bar is divided into multiple sections. When a first frame signal of a panel is applied to scan the first section, the LEDs of the first section are lit, while the remaining is set off. When the panel signal scans the second section, only the LEDs of the second section are lit. This is also applied to the other sections. Such an operation is carried out for each frame. The performance of the shutter glass 3D displaying is assessed according to cross-talking among sections. The lower the cross-talking is, the better the displaying result will be. Cross-talking is generally determined according to cross talk among the backlight sections and design of timing sequence.
Cross-talking among backlight sections generally comes from the influence of brightness among different sections and the best situation is that when one section is lit, the backlighting of all the remaining sections shows darkness. As shown in FIG. 1, a side elevational view of a conventional light guide plate with upper microstructures is illustrated. Forming serrated microstructures on the upper or lower surface of a light guide plate is a commonly known design. FIG. 1 is made for observation of light guide plate 10 from the side where light gets incident. The upper surface of the light guide plate 10 forms upper microstructures 11 distributed on the upper surface of the light guide plate 10 in a successive raising-recessing-alternating arrangement in a direction perpendicular to the propagation direction of light in the light guide plate 10, whereby the geometric variation on the upper surface of the light guide plate is useful to eliminate the conditions for occurrence of total reflection. As shown in FIG. 2, a schematic view illustrating difference of light shape between a conventional flat light guide plate and a light guide plate with upper microstructures is given. Although FIG. 2 illustrates that the light shape of the light guide plate 20 with upper microstructures shows a more confined light shape than a flat light guide plate 21, yet actually, even though light in the light guide plate 20 with upper microstructures is partially confined, it gets diverging to some extents.
With the increase of the propagation distance, the divergence of the light shape gets greater and imposes severer influence on other sections. As shown in FIG. 3, a schematic view showing the distribution of light field of a well known upper-microstructured light guide plate 30 for the condition of one section being lit is given. When one section of the upper-microstructured light guide plate 30 is lit, the light shape is getting divergent with distance. Referring to FIG. 4, which is a schematic view showing the distribution of brightness in a vertical direction for the light shape shown in FIG. 3, the brightness distribution in the vertical direction can be indicated by full width at half maximum (FWHM), left hand side being the light incidence side. Referring to FIG. 5, which is a schematic view showing the variation of the width for half brightness at different locations with respect to the distance, in single short edge light incidence, FWHM shows a trend of getting wider with the increase of distance. In other words, for single short edge light incidence, the remote side shows severer cross-talking than the light incidence side.
Referring to FIG. 6, a schematic view showing the structure of a conventional side-edge LED light bar is given. The LED light bar 60 shown in FIG. 6 is divided into two sections 63, 64. The distribution of LEDs 61 on the conventional side-edge LED light bar 60 is not arranged in any specific design according to the sections. It is often that the LEDs 61 are set at a fixed pitch 62.
An LED light bar with such an arrangement shows severe cross-talking between different sections when applied to backlight modules of singe short edge incidence or dual short edge incidence. As shown in FIGS. 7 and 8, which are schematic views showing overlapping of backlighting light fields in backlight modules of singe short edge incidence and dual short edge incidence, in which overlapping of the backlighting light fields of four sections is shown. FIG. 7 is associated with the backlight module of singe short edge incidence, in which an LED light bar 71 is set at a short edge of a light guide plate 70. FIG. 8 is associated with the backlight module of dual short edge incidence, in which LED light bars 81, 82 are respectively set at two opposite short edges of a light guide plate 80. In FIGS. 7 and 8, the light field distributions of different sections of the light bar are respectively indicated by dot-dash line, dash line, and solid line for distinction. The crossing portion between light fields of different sections is shown great, which means cross-talking is severe. The light bars in FIGS. 7 and 8 are both divided into four light bar sections, in which sections 1-4 represent four sections and are respectively indicated by a dot-dash line, a dash line, a solid line, and a dot-dash line. These different types of line (namely the dot-dash line, the dash line, the solid line, and the dot-dash line) in the drawings respectively indicate the border of half maximum brightness for the section. The overlapping portion between two sections is a cross range shown in the drawings. The greater the cross range is, the severer the cross-talking between the sections will be and the poor the 3D displaying performance will be.